Recently, a curtain airbag device is mounted on more and more vehicles, such as automobiles, wherein when a side collision has occurred on the vehicle, the curtain airbag device protects a passenger by spreading a bag body called an airbag into a curtain shape between a vehicle interior lateral part and the passenger (for example, refer to Patent Document 1).
The airbag main body of the curtain airbag device disclosed by Patent Document 1, which spreads into a curtain shape along a vehicle interior lateral part, includes an expanding portion formed in the protection area of a passenger and an auxiliary chamber formed outside the protection area. The expanding portion and the auxiliary chamber communicate with each other through a gas communicating passage called a venting hole. When the inner pressure of the expanding portion increases by a load of the airbag main body having expanded upon input of a shock, the load restraining a passenger, a part of gas in the expanding portion flows in into the auxiliary chamber through the venting hole. Thus, the pressure in the expanding portion decreases to thereby reduce the peak acceleration on the passenger.